Bodies of hardenable synthetic-resin materials, such as polyesters, epoxy resins and like thermosetting materials are commonly reinforced with fibers or fabric (textile) structures of glass filaments, synthetic-resin fibers or metal strands.
Such bodies have been made heretofore either by the so-called wet process or by the so-called dry process.
In the wet process, the synthetic-resin impregnated fibers, e.g. in the form of roving, can be coiled upon a core having an outer profile corresponding to the inner profile of the body to be fabricated.
When staple fibers are used as the reinforcing material, the impregnated fibers can be sprayed upon a mold wall.
In the case of reinforcing fiber webs of woven or nonwoven fibrous material, the latter can be impregnated with the synthetic-resin material and applied to the form or mold wall or to a previous layer of the impregnated fibers applied to such a wall. Rolling or like compaction can then be carried out to ensure complete freedom of the layer from air bubbles.
The aforementioned compaction, densification or compression, in all cases to ensure freedom from trapped air bubbles, is generally of limited applicability as the body shape becomes more complex and is frequently uncontrolable so that uniform-quality bodies cannot be produced economically by these techniques.
In the dry process, the fibers are first applied to the mold, i.e. given the desired shape, for example, by coiling them upon a mold core, whereupon they are impregnated with the synthetic-resin material.
In order to ensure a high density and thus freedom from air bubbles in the latter case, it is a common practice to apply the fiber coils to the mold core and to set the latter in a mold cavity which is then evacuated, filled with the synthetic-resin material, pressurized to press the synthetic-resin material into the interstices of the fiber, and the synthetic-resin material is permitted to harden.
While this technique has been found to give rise to shaped bodies which are practically completely free from air bubbles and have a high density, the disadvantage of this process is that expensive molds must be used both because the mold must be vacuum and pressure tight and provided with feed and discharge lines, but also because the hardening time of the synthetic-resin material may be relatively long. For a given output rate, therefore, industrial production by this technique requires, as a rule, a multiplicity of expensive molds.